Up on Blackheath this week it’s all compositing toilets this and global warming that. They have a point, these climate campers, as it appears that the production of animal manure is increasing concentrations of nitrous oxide (aka laughing gas) in the atmosphere.
Nitrous oxide concentrations have been increasing since the industrial revolution, and this potent greenhouse gas now accounts for around 6% of total anthropogenic global warming. So says Eric Davidson, a soil biologist at the Woods Hole Research Center in Massachusetts.
Most of the atmospheric nitrous oxide is the result of microbial production in soils, and this has increased with the use of petrochemical-derived nitrogen fertilisers in agriculture. But fertiliser use cannot alone account for the rising concentrations of nitrous oxide.
In his study for Nature Geoscience, Davidson modelled atmospheric concentrations of nitrous oxide, industrial sources of the gas, and fertiliser and manure production since 1860. Before then, agricultural expansion and livestock production may have led to a globally significant mining of soil nitrogen, which fuelled a steady increase in nitrous oxide.
Davidson shows that an increase in animal manure production can explain much of the rise in atmospheric nitrous oxide over the past century and a half. His conclusion is that, given the increasing global demand for meat, nitrous oxide emissions from manure should be managed.
How about reducing the demand for meat?
Eric A Davidson, “The contribution of manure and fertilizer nitrogen to atmospheric nitrous oxide since 1860”, Nature Geoscience 30 August 2009